This is a manhole with the symbol of Oslo on it. It's Saint Halvard, the patron of Oslo. In his hand he's holding the three arrows that killed him and the millstone his killers used to sink him in the sea. He sits on a throne with lion heads and before his feet lies the woman who symbolises the victim he tried to save.
The story is that on May 15th in the year 1043, a woman was accused of stealing, but claimed she hadn't. She tried to escape and begged a young man, Halvard, to take her on his boat across the sea. He believed her and helped her, but the followers soon reached them on another boat and accused Halvard of helping a thief. He wouldn't listen to them, so they shot him with arrows and then beat the woman to death. To cover up the murders, the woman was buried near the beach and Halvard was dumped in the sea with a millstone around his neck. But his body floated and was found.
Later, at his grave, there were reported several omens. Halvard was martyrized as he had died trying to save an innoncent woman, and was eventually named a saint. His remains were later placed in a silver shrine and placed in the Maria church in Oslo.
In the year 1130, the new Saint Halvard church was built and the holy shrine was moved there.